This invention relates to power amplifier circuits with fault detection and, in particular, for fault detection for power amplifiers with combined power amplifier modules that are driven by a power splitter and their outputs combined by a power combiner.
The standard method of employing an N array of hybrid power splitters and combiners to combine N amplifiers offer some sort of degradation performance when one or more of the power amplifiers fails.
In an article published in the IEEE Transactions on Microwave Theory and Techniques, Volume NTT-28, No. 10, October 1980 entitled "Improving the Graceful-Degradation Performance of Combined Power Amplifiers" by Adel A. M. Saleh, it was disclosed that the degradation to the combined circuit caused by the failed amplifier would be minimized by either shorting the input of a power combiner that is connected to a failed amplifier, or opening the combiner circuit of the failed amplifier.
A corporate amplifier is defined as and includes a plurality of N amplifier modules where N is a positive integer that is greater than one. The plurality of amplifier modules are driven by a power splitter which takes a signal that is to be amplified and divides it into N equal amplitude components. Each component is applied to a member of the plurality of N amplifier modules for amplification. The outputs of the power amplifier modules are combined by a power combiner that has N input terminals with each input terminal being connected to an output terminal of a member of the plurality of N amplifier modules. A fault detector detects failure of one or more of the plurality of N amplifier modules and provides a fault signal indicating thereby a failed amplifier module. A compensation circuit compensates both the power splitter and the power combiner means so that if a fault is detected in one or more of the plurality of N amplifier modules the performance of the corporate amplifier will be optimized.
A fault or a failure of an amplifier module is detected by sensing the DC current drawn by an amplifier module to obtain a sense signal for each amplifier module. These sense signals are averaged by an averaging circuit to determine an average current level which is used as a reference signal. A window, comprising an upper level and a lower level, is established in the reference signal as well as in each of the individual sense signals. A plurality of N comparators compares each sense signal's upper level and lower level with the average signal's upper level and lower level to ascertain if the the current produced by amplifier module represented by the sense signal is drawing a current level which is outside of the preordained DC current window which indicates an amplifier module fault. A high level comparison and a low level comparison is made. The results of these comparisons are OR'd together to obtain a fault signal which is used to compensate both the power splitter and the power combiner for the fault so as to optimize the performance of the corporate amplifier.
Depending on the power splitter and power combiner type, the compensation circuit will remove the faulted amplifier module from the circuit. If the balance resistor, used to balance each array with its neighbors, has a large resistance value such as infinity, both the output terminal of the power splitter and the input terminal of the power combiner will be shorted. Alternatively, if the balancing resistors have a low resistance such as zero ohms, the output terminal of the power splitter and the input terminal of the power combiner are opened.
It is the object of this invention to provide a corporate amplifier that includes a plurality of combined amplifier modules and wherein if one amplifier module should fail, that fault will be detected and compensation will be provided to the power splitter that drives the plurality of amplifier modules and to the power combiner that combines the output of the power amplifier modules such that there will be equal load sharing of the remaining amplifier modules following an amplifier module failure.
It is another object of the invention to provide a corporate amplifier that includes a plurality of combined amplifier modules that are divided and then recombined after amplification by a power splitter and power combiner in which the power splitter and power combiner have a balance resistance equal to zero in one embodiment and infinity in a second embodiment.